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Synthesis of (±)-Leonuketal
Key words(±)-leonuketal - 8,9-seco-labdane terpenoid - titanium catalysis - Shapiro reaction - fragmentation - gold catalysis - spiroketalization
The tetracyclic 8,9-seco-labdane terpenoid (−)-leonuketal was isolated from the Chinese liverwort Leonurus japonicus and shows significant vasorelaxant activity against KCl-induced contraction of rat aorta. The authors present the first total synthesis relying on a Ti-mediated cyclization, a Shapiro reaction–fragmentation and an Au-catalyzed spirocyclization.
Epoxide A was subjected to Ti-mediated radical cyclization to obtain bicyclic ketone B. Shapiro reaction–fragmentation was applied to furnish alkyne D. Alkylation of ketoester F with iodide E afforded alkyne G which was cyclized to butenolide H. Au-catalyzed spirocyclization delivered spiroketal I which was transformed into the natural product in additional 9 steps.
16 December 2020 (online)
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